The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.
A clone is generally understood as a population of cells which has descended from a common precursor cell. Diagnosis and/or detection of the existence of a clonal population of cells or organisms in a subject has generally constituted a relatively problematic procedure. Specifically, a clonal population may constitute only a minor component within a larger population of cells or organisms. For example, in terms of the mammalian organism, one of the more common situations in which detection of a clonal population of cells is required occurs in terms of the diagnosis and/or detection of neoplasms, such as cancer. However, detection of one or more clonal populations may also be important in the diagnosis of conditions such as myelodysplasia or polycythaemia vera and also in the detection of antigen driven clones generated by the immune system.
Generally, the population within which the clone arises corresponds to a population of cells within a particular tissue or compartment of the body. Nevertheless, despite the fact that sampling such a population of cells effectively narrows the examination to a sub group of cells or organisms, this may nevertheless still present a clinician with a large background population of non-clonal cells or organisms within which the clonal population must be identified.
If the members of the clone are characterized by a molecular marker, such as an altered sequence of DNA, then the problem of detection may be able to be translated into the problem of detecting a population of molecules which all have the same molecular sequence within a larger population of molecules which have a different sequence, either all being the same and different, or being heterogeneous to a greater or lesser extent. The level of detection of the marker molecules that can be achieved is very dependent upon the sensitivity and specificity of the detection method, but nearly always, when the proportion of target molecules within the larger population of molecules becomes small, the signal noise from the larger population makes it impossible to detect the signal from the target molecules.
Accordingly, there is a need to develop improved methods for qualitatively and/or quantitatively detecting the existence of a clonal population of cells within any biological context (ie. irrespective of the level of non-clonal background cellular material), which methods are highly sensitive yet simple to routinely perform.
In work leading up to the present invention, it has been determined that the marker sequence of interest, to which the detection method is directed, is situated in a single region of the genome and is usually flanked by unique sequences. In particular, it has been determined that the marker of interest is often flanked on one or both sides by unique sequences which correspond to one or two members of a family of repeated sequences. To the extent that the different members of each subject family of repeated sequences themselves differ in sequence, it has been determined that those sequences provide a unique means of analysing, for example characterising, detecting, isolating or quantifying, a marker sequence of interest. It has also been determined that such sequences can be routinely and simply identified by any suitable methods such as microassay-related methodology or PCR. In relation to the latter, for example, one can conduct a multiplicity of amplification reactions which each differ in the context of the primer pair comprising that reaction. Specifically, by designing primer pairs wherein one primer is common to all reactions and is directed to a conserved region, such as a consensus sequence, of one flanking sequence and the other primer is selected from a group of primers such that each individual member of the group is specific for each individual member of a family of repeated sequences, it can be clearly and easily determined which two members of the family of repeated sequences flank the marker nucleic acid molecule characterising the clonal population of interest. Such principles can also be applied in the context of other platform technologies, such as chip-based microassays which comprise an array of probes specifically directed to each member of a family of repeated sequences. The development of this method thereby facilitates a means of detecting and/or monitoring the subject clonal population of cells, even in the context of a large non-subject-clonal background cellular population, by providing a means of specifically enriching for said marker sequences utilising the primers identified in accordance with the method of the present invention.